(1) Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a characteristic checking element in addition to a regular element in the device.
(2) Description of the Prior Art
In the prior art semiconductor device, there was provided on a semiconductor wafer a pattern for checking a contact resistance, a threshold voltage and current-voltage (I-V) characteristics of a transistor so that characteristic variations attributable to fabrication and characteristic abnormalities due to an accident could easily be checked without the need of the P/W check (pellet test at a wafer stage) of a product.
FIG. 1A is a plan view of a prior art MOS transistor for characteristic checking and FIG. 1B is a sectional view thereof taken on line A--A in FIG. 1A. As seen from these figures, the prior art characteristic checking semiconductor device (MOS transistor) has the following configuration. A gate oxide film 3 and a gate electrode 4 are formed in a device region surrounded by a field oxide film 2 on a p-type semiconductor substrate 1, and n.sup.+ -type diffused layers 6 serving as source/drain regions are formed using the gate electrode 4 as a mask. An interlayer insulating film 7 is formed, and a plurality of contact holes 8 are opened through it. Aluminum (Al) interconnection layers 9 are formed which is kept in contact with the n.sup.+ -diffused layers 6 and the gate electrode 4, respectively. It should be noted that the Al interconnection layer is not shown in FIG. 1A.
The above prior art characteristic checking transistor (pattern) has the following defect. The gate electrode thereof is independent and isolated and is disposed differently from regular gate electrode patterns in a semiconductor device. For this reason, the gate electrode of the checking transistor pattern, which suffers from the influence of "micro-loading effect" in lithography and etching, has a different resultant size from that of the regular gate electrode within the device. The "micro-loading effect" means that, in patterning, lithography and etching are influenced by the size and density of a pattern area so that the shape and size of the pattern cannot be made uniform.
Thus, the characteristic checking transistor provided for the purpose of monitoring the characteristic of the regular transistor within the device cannot be representative of that characteristic. This presents problems in the controlling of the fabrication process.